Soil resistance work is carried out by archaeologists from the University of Leicester at the stone circle site in Avebury
Photograph: Dr Mark Gillings/University of L/PA

A mysterious square formation has been discovered within the Neolithic stone circle monument at Avebury, rewriting the narrative of one of the wonders of the prehistoric world.

Archaeologists believe the hidden stones, discovered using radar technology, were one of the earliest structures at the site and may have commemorated a Neolithic building dating to around 3500 BC.

Previously archaeologists had speculated that the vast stone outer circle, which at 330 metres in diameter is the largest in Europe, had been built from the outside inwards. The latest work suggests that a lowly wooden building, that may have served as a focal point for the Neolithic community, seeded the monument, with a consecutive series of stone structures springing up around it over hundreds of years.

Mark Gillings, an archaeologist at the University of Leicester who led the work, told the Guardian: “Our working interpretation is that the house is the first thing. It falls into ruin but they’re still remembering and respecting it. They put a square around it about 3000 BC and then the circles. It’s like ripples on a pond coming out from the house.”

A model of the inner square at the Avebury Neolithic stone circl. Photograph: Mark Gillings / University of Leicester

Gillings and colleagues mapped out the positions of the prehistoric standing stones, which they believe were hidden and buried, along with the positions of others likely destroyed during the 17th and 18th centuries. Normally henge monuments like Stonehenge and Avebury are round, making the new formation, which has been buried for hundreds of years, highly unusual and possibly explaining why the significance of the stones had been overlooked until now.

Clues to the existence of a square structure, each side of which was around 30 metres in length, were first discovered by the archaeologist and marmalade magnate, Alexander Keiller, who carried out an excavation at the site in 1939. This revealed a number of small standing stones placed in a line close to a 6-metre upright stone known as the Obelisk.

Keiller’s excavation also revealed postholes and grooves in the ground, indicating that a building had once been there.

“He concluded that it was a strange medieval lean-to cattle shed,” said Gillings.

However, when the newly discovered square was compared with Keiller’s notes they found that the stones were centred on and aligned with the building, suggesting that it was Neolithic in origin. More recently similar Neolithic buildings have been discovered at other sites and archaeologists believe they probably acted as a focal point for communities, although whether they would have lived in the structures, held meetings, carried out rituals or stored things is unknown.

Archaeologists unearth prehistoric ritual area around Bryn Celli Ddu

Read more

“It completely changes the narrative. The seed might have been in the form of a small inconspicuous house,” said Gillings. The commemoration gradually got more dramatic and in your face and by 2,000 BC you’ve got stones everywhere.”

Nick Snashall, National Trust archaeologist at Avebury, said: “This discovery has been almost 80 years in the making but it’s been well worth waiting for. The completion of work first started by Keiller in the 1930s has revealed an entirely new type of monument at the heart of the world’s largest prehistoric stone circle, using techniques he never dreamed of.”

And might the new discoveries justify fresh excavations at the site?

“Hell yeah,” said Gillings. “If this doesn’t I don’t know what would. We’d like to go in and excavate and tease out more of the details.”